Real-time Risk-averse Dispatch of an Integrated Electricity and Natural Gas System via Condi-tional Value-at-risk-based Lookup-table Ap-proximate Dynamic Programming

The real-time risk-averse dispatch problem of an integrated electricity and natural gas system(IEGS)is studied in this paper.It is formulated as a real-time conditional value-at-risk(CVaR)-based risk-averse dis-patch model in the Markov decision process framework.Because of its stochasticity,nonconvexity and nonlinearity,the model is difficult to analyze by traditional algorithms in an acceptable time.To address this non-deterministic polynomial-hard problem,a CVaR-based lookup-table approximate dynamic programming(CVaR-ADP)algo-rithm is proposed,and the risk-averse dispatch problem is decoupled into a series of tractable subproblems.The line pack is used as the state variable to describe the impact of one period’s decision on the future.This facilitates the reduction of load shedding and wind power curtailment.Through the proposed method,real-time decisions can be made according to the current information,while the value functions can be used to overview the whole opti-mization horizon to balance the current cost and future risk loss.Numerical simulations indicate that the pro-posed method can effectively measure and control the risk costs in extreme scenarios.Moreover,the decisions can be made within 10 s,which meets the requirement of the real-time dispatch of an IEGS.Index Terms—Integrated electricity and natural gas system,approximate dynamic programming,real-time dispatch,risk-averse,conditional value-at-risk.

Reliability Assessment of Integrated Electricity and Natural Gas Transmission Systems in Presence of Power-to-gas and Combined Heat and Power Technologies

Assessing the reliability of integrated electricity and gas systems has become an important issue due to the strong dependence of these energy networks through the power-to-gas(P2G)and combined heat and power(CHP)technologies.The current work,initially,presents a detailed energy flow model for the integrated power and natural gas system in light of the P2G and CHP technologies.Considering the simultaneous load flow of networks,a contingency analysis procedure is proposed,and reliability is assessed through sequential Monte Carlo simulations.The current study examines the effect of independent and dependent operation of energy networks on the reliability of the systems.In particular,the effect of employing both P2G and CHP technologies on reliability criteria is evaluated.In addition,a series of sensitivity analysis are performed on the size and site of these technologies to investigate their effects on system reliability.The proposed method is implemented on an integrated IEEE 24-bus electrical power system and 20-node Belgian natural gas system.The simulation procedure certifies the proposed method for reliability assessment is practical and applicable.In addition,the results prove connection between energy networks through P2G and CHP technologies can improve reliability of networks if the site and size of technologies are properly determined.

Optimal Operation of Integrated Energy Systems Subject to Coupled Demand Constraints of Electricity and Natural Gas

This paper proposes a hybrid multi-objective optimization and game-theoretic approach(HMOGTA)to achieve the optimal operation of integrated energy systems(IESs)consisting of electricity and natural gas(E&G)utility networks,multiple distributed energy stations(DESs),and multiple energy users(EUs).The HMOGTA aims to solve the coordinated operation strategy of the electricity and natural gas networks considering the demand characteristics of DESs and EUs.In the HMOGTA,a hierarchical Stackelberg game model is developed for generating equilibrium strategies of DESs and EUs in each district energy network(DEN).Based on the game results,we obtain the coupling demand constraints of electricity and natural gas(CDCENs)which reflect the relationship between the amounts and prices of electricity and cooling(E&C)that DESs purchase from utility networks.Furthermore,the minimization of conflicting costs of E&G networks considering the CDCENs are solved by a multi-objective optimization method.A case study is conducted on a test IES composed of a 20-node natural gas network,a modified IEEE 30-bus system,and 3 DENs,which verifies the effectiveness of the proposed HMOGTA to realize fair treatment for all participants in the IES.

Cascading Failure Propagation Simulation in Integrated Electricity and Natural Gas Systems

The sharp increase in the total installed capacity of natural gas generators has intensified the dynamic interaction between the electricity and natural gas systems,which could induce cascading failure propagation across the two systems that deserves intensive research.Considering the distinct time response behaviors of the two systems,this paper discusses an integrated simulation approach to simulate the cascading failure propagation process of integrated electricity and natural gas systems(IEGSs).On one hand,considering instantaneous re-distribution of power flows after the occurrence of disturbance or failure,the steady-state AC power flow model is employed.On the other hand,gas transmission dynamics are represented by dynamic model to capture the details of its transition process.The interactions between the two systems,intensified by energy coupling components(such as gas-fired generator and electricity-driven gas compressor)as well as the switching among the operation modes of compressors during the cascading failure propagation process,are studied.An IEGS composed of the IEEE 30-bus electricity system and a 14-node 15-pipeline gas system is established to illustrate the effectiveness of the proposed simulation approach,in which two energy sub-systems are coupled by compressor and gas-fired generator.Numerical results clearly demonstrate that heterogeneous interactions between electricity and gas systems would trigger the cascading failure propagation between the two coupling systems.

Robust optimization for improving resilience of integrated energy systems with electricity and natural gas infrastructures

The integration of natural gas in electricity network requires a more reliable operating plan for increasing uncertainties in the whole system. In this paper, a threestage robust optimization model is proposed for resilient operation of energy system which integrates electricity and natural gas transmission networks with the objective of minimizing load curtailments caused by attacks. Nonconvex constrains are linearized in order to formulate the dual problem of optimal energy flow. Then, the proposed three-stage problem can be reformulated into a two-stage mixed integer linear program(MILP) and solved by Benders decomposition algorithm. Numerical studies on IEEE30-bus power system with 7-node natural gas network and IEEE 118-bus power system with 14-node natural gas network validate the feasibility of the proposed model for improving resilience of integrated energy system. Energy storage facilities are also considered for the resiliency analysis.

Stochastic Dynamic Economic Dispatch of Wind-integrated Electricity and Natural Gas Systems Considering Security Risk Constraints

As the proportion of wind power generation increases in power systems,it is necessary to develop new ways for wind power accommodation and improve the existing power dispatch model.The power-to-gas technology,which offers a new approach to accommodate surplus wind power,is an excellent way to solve the former.Hence,this paper proposes to involve power-to-gas technology in the integrated electricity and natural gas systems(IEGSs).To solve the latter,on one hand,a new indicator,the scale factor of wind power integration,is introduced into the wind power stochastic model to better describe the uncertainty of grid-connected wind power;on the other hand,for quantizing and minimizing the impact of the uncertainties of wind power and system loads on system security,security risk constraints are established for the IEGS by the conditional value-at-risk method.By considering these two aspects,an MILP formulation of a security-risk based stochastic dynamic economic dispatch model for an IEGS is established,and GUROBI obtained from GAMS is used for the solution.Case studies are conducted on an IEGS consisting of a modified IEEE 39-bus system and the Belgium 20-node natural gas system to examine the effectiveness of the proposed dispatch model.

Integrated coordination scheduling framework of electricity-natural gas systems considering electricity transmission N—1 contingencies and gas dynamics

This paper discusses a security-constrained integrated coordination scheduling framework for an integrated electricity-natural gas system(IEGS),in which both tight interdependence between electricity and natural gas transmission networks and their distinct dynamic characteristics at different timescales are fully considered.The proposed framework includes two linear programming models.The first one focuses on hour-based steady-state coordinated economic scheduling on power outputs of electricity generators and mass flow rates of natural gas sources while considering electricity transmission N-1 contingencies.Using the steady-state mass flow rate solutions of gas sources as the initial value,the second one studies second-based slow gas dynamics and optimizes pressures of gas sources to ensure that inlet gas pressure of gas-fired generator is within the required pressure range at any time between two consecutive steady-state scheduling.The proposed framework is validated via an IEGS consisting of an IEEE 24-bus electricity network and a15-node 14-pipeline natural gas network coupled by gasfired generators.Numerical results illustrate the effectiveness of the proposed framework in coordinating electricity and natural gas systems as well as achieving economic and reliable operation of IEGS.

Integrated operational planning of hydrothermal power and natural gas systems with large scale storages

The growing installation of natural gas fired power plants has increased the integration of natural gas and electricity sectors. This has driven the need investigate the interactions among them and to optimize energy resources management from a centralized planning perspective. Thus, a combined modeling of the reservoirs involved in electric power and gas systems and their locations on both networks are essential features to be considered in the operational planning of energy resources.This paper presents a modeling and optimization approach to the operational planning of electric power and natural gas systems, taking into account different energy storage facilities, such as water reservoirs, natural gas storages and line packs of pipelines. The proposed model takes advantage of captures both energy systems synergy and their associated networks. This approach identifies the interactions between the energy storage facilities and their economic impact over their optimal scheduling. The results show the benefits of an integrated operational planning of electric power and natural gas systems, the close interdependency between the energy resources stored in both systems, and the effects of a combined scheduling.

Optimal Energy Reserve Scheduling in Integrated Electricity and Gas Systems Considering Reliability Requirements

With the growing interdependence between the electricity system and the natural gas system,the operation uncertainties in either subsystem,such as wind fluctuations or component failures,could have a magnified impact on the reliability of the whole system due to energy interactions.A joint reserve scheduling model considering the cross-sectorial impacts of operation uncertainties is essential but still insufficient to guarantee the reliable operation of the integrated electricity and natural gas system(IEGS).Therefore,this paper proposes a day-ahead security-constrained unit commitment(SCUC)model for the IEGS to schedule the operation and reserve simultaneously considering reliability requirements.Firstly,the multi-state models for generating units and gas wells are established.Based on the multi-state models,the expected unserved energy cost(EUEC)and the expected wind curtailment cost(EWC)criteria are proposed based on probabilistic methods considering wind fluctuation and random failures of components in IEGS.Furthermore,the EUEC and EWC criteria are incorporated into the day-ahead SCUC model,which is nonconvex and mathematically reformulated into a solvable mixed-integer second-order cone programming(MISOCP)problem.The proposed model is validated using an IEEE 30-bus system and Belgium 20-node natural gas system.Numerical results demonstrate that the proposed model can effectively schedule the energy reserve to guarantee the reliable operation of the IEGS considering the multiple uncertainties in different subsystems and the cross-sectorial failure propagation.

电-气互联系统仿射能流交替递归计算方法

在源荷不确定性日益显著的背景下,不确定性能流计算对电-气互联系统能源优化调度具有重要意义。针对天然气网络仿射能流算法面临的仿射数矩阵求逆运算复杂、难以适用环网等问题,该文提出一种天然气网络全纯嵌入仿射能流方法。在此基础上,根据耦合设备处的能量流动对电、气子系统能流方程进行重构,构建全纯嵌入的电-气仿射多能流模型。为降低多能流计算的初值依赖性、提升多能流计算效率,提出一种仿射能流交替递归计算方法,将电网空载状态的状态量初值作为多能流计算起始点,基于各仿射型状态量的幂级数系数递推关系,以交替进行的方式逐阶递归计算电网、气网和耦合设备的仿射型状态量幂级数系数,求解电-气互联系统的能流分布区间。仿真结果验证了所提方法在算法保守性、收敛性和计算效率等方面的优势。

电-气互联系统预测-校正型仿射能流算法

综合能源系统能流耦合渐趋紧密,与此同时可再生能源和负荷需求的强不确定性对系统能流分析提出了挑战。因此,提出一种电-气互联系统(IEGS)仿射型区间能流算法,在仿射能流计算结果中保留噪声元特征,通过噪声元系数分析各独立不确定因素对系统状态变量的影响程度。建立电、气子系统仿射模型及能流方程。提出基于域收缩思想的IEGS预测-校正型仿射能流算法,根据灵敏度对状态量的解域进行保守的预测,并构建优化模型对解域进行压缩校正。同时,采用多能流分布式迭代方法进行求解,其无须考虑复杂耦合网络中的多能流计算顺序。最后通过仿真验证了所提方法在保守性、计算效率方面的优势,并量化分析了不确定因素对系统状态量的影响。

考虑氢混燃机动态混氢特性的电-气互联系统优化调度

电–气互联系统是综合能源系统的重要组成部分,燃气机组是其中关键的能源耦合元件,而随着能源系统低碳化转型,燃气机组掺氢燃烧发电的技术应运而生。传统氢混燃机相关研究大多只考虑固定掺氢比运行的情况,并未考虑机组动态调整掺氢比运行的影响。传统电–气互联系统优化调度相关研究主要面向运行经济性,而对计及氢混燃机的能量与备用统一出清鲜有研究。为此,该文提出了一种考虑氢混燃机动态混氢比的电–气互联系统优化调度方法,基于动态混氢特性建立氢混燃机精细化模型,并通过电解水制氢技术为氢混燃机提供氢气来源,配置储氢罐和储气罐作为联合体为系统提供备用;采用二项式松弛方法对氢混燃机耗气流量方程进行线性转化,将原有非凸非线性模型转化为混合整数线性规划模型求解;最后通过仿真验证所提方法的有效性,分析不同场景下系统运行状态,实现了“风电–电解水制氢–氢混燃机”模式下风电消纳潜力的深度挖掘。

Bi-Level Bidding and Multi-Energy Retail Packages for Integrated Energy Service Providers Considering Multi-Energy Demand Elasticity

How to effectively use the multi-energy demand elasticity of users to bid in the multi-energy market and formulate multi-energy retail packages is an urgent problem which needs to be solved by integrated energy service providers(IESPs)to attract more users and reduce operating costs.This paper presents a unified clearing of electricity and natural gas based on a bi-level bidding and multi-energy retail price formulation method for IESPs considering multi-energy demand elasticity.First,we propose an operating structure of IESPs in the wholesale and retail energy markets.The multi-energy demand elasticity model of retail-side users and a retail price model for electricity,gas,heat and cooling are established.Secondly,a bi-level bidding model for IESPs considering multi-energy demand elasticity is established to provide IESPs with wholesale-side bidding decisions and retail-side energy retail price decisions.Finally,an example is given to verify the proposed method.The results show that the method improves the total social welfare of the electricity and natural gas markets by 7.99%and the profit of IESPs by 1.40%.It can reduce the variance of the electricity,gas,and cooling load curves,especially the reduction of the variance of the electricity load curve can which reach 79.90%.It can be seen that the research in this paper has a positive effect on repairing the limitations of integrated energy trading research and improving the economics of the operation of IESPs.

Active-reactive power scheduling of integrated electricity-gas network with multi-microgrids

Advances in natural gas-fired technologies have deepened the coupling between electricity and gas networks,promoting the development of the integrated electricity-gas network(IEGN)and strengthening the interaction between the active-reactive power flow in the power distribution network(PDN)and the natural gas flow in the gas distribution network(GDN).This paper proposes a day-ahead active-reactive power scheduling model for the IEGN with multi-microgrids(MMGs)to minimize the total operating cost.Through the tight coupling relationship between the subsystems of the IEGN,the potentialities of the IEGN with MMGs toward multi-energy cooperative interaction is optimized.Important component models are elaborated in the PDN,GDN,and coupled MMGs.Besides,motivated by the non-negligible impact of the reactive power,optimal inverter dispatch(OID)is considered to optimize the active and reactive power capabilities of the inverters of distributed generators.Further,a second-order cone(SOC)relaxation technology is utilized to transform the proposed active-reactive power scheduling model into a convex optimization problem that the commercial solver can directly solve.A test system consisting of an IEEE-33 test system and a 7-node natural gas network is adopted to verify the effectiveness of the proposed scheduling method.The results show that the proposed scheduling method can effectively reduce the power losses of the PDN in the IEGN by 9.86%,increase the flexibility of the joint operation of the subsystems of the IEGN,reduce the total operation costs by $32.20,and effectively enhance the operation economy of the IEGN.

Coordinated optimal dispatch and market equilibrium of integrated electric power and natural gas networks with P2G embedded

As power to gas(P2 G) technology gradually matures, the coupling between electricity networks and natural gas networks should ideally evolve synergistically.With the intent of characterizing market behaviors of integrated electric power and natural gas networks(IPGNs)with P2 G facilities, this paper establishes a steady-state model of P2 G and constructs optimal dispatch models of an electricity network and a natural gas network separately. In addition, a concept of slack energy flow(SEF) is proposed as a tool for coordinated optimal dispatch between the two networks. To study how the market pricing mechanism affects coordinated optimal dispatch in an IPGN, a market equilibrium-solving model for an IPGN is constructed according to game theory, with a solution based on the Nikaido-Isoda function. Case studies are conducted on a joint model that combines the modified IEEE 118-node electricity network and the Belgian 20-node gas network.The results show that if the game between an electric power company and a natural gas company reaches market equilibrium, not only can both companies maximize their profits, but also the coordinated operation of the coupling units, i.e., gas turbines and P2 G facilities, will contribute more to renewable energy utilization and carbon emission reduction.

考虑碳排放和混合燃烧特性的氢混燃机精细化建模及应用

随着混氢天然气技术发展,氢混燃机成为未来电-混氢天然气城市综合能源系统的关键技术节点。为此,该文分别对混氢天然气网和氢混燃机进行特性分析,并搭建考虑多气体组分混合的混氢天然气网与氢混燃机耦合架构。从多学科信息融合角度出发,采用阿伦尼乌斯方程和系统热力学分别对氢混燃机的碳排放和混合燃烧出力特性精细化建模,并基于实例参考范围验证所提模型的合理性。在此基础上,将氢混燃机模型应用到优化调度中,以系统总运行成本最低为目标函数,计及城市配电网、混氢天然气网以及用户单元内部运行约束,建立电-混氢天然气城市综合能源系统优化调度模型。以耦合混氢天然气系统的某实际城市配电网为算例进行验证,结果表明,基于电转气的天然气网掺氢运输和本地储氢供应均能有效提高电网的可再生能源消纳水平,其风电利用率之差不超过2.12%,但前者的总运行成本比后者少4.31%,能够降低系统总运行成本的同时有效促进用户侧低碳减排。

电-氢-混氢天然气耦合的城市综合能源系统低碳优化调度

混氢天然气(HCNG)技术可有效解决大规模电制氢面临的纯氢运输成本高的问题。针对大规模风光消纳与城市综合能源系统(UIES)低碳优化调度问题,在源-网-荷-氢协同优化框架下,提出考虑电-氢-HCNG耦合与需求响应的UIES低碳优化调度方法。对电-氢-HCNG耦合单元运行特性进行建模,并引入用户单元需求响应机制,以系统运行成本最小为目标,建立UIES低碳优化调度模型。通过算例分析对所提模型进行验证,结果表明电-氢-HCNG耦合单元与用户单元需求响应机制的引入能够有效促进风光消纳,提高UIES低碳性。

负荷重分配攻击下电–气系统损失评估与脆弱性分析

在电力信息物理系统中,负荷重分配(load redistribution,LR)攻击是一种常见的虚假数据注入攻击。而在天然气网与电网耦合紧密的背景下,针对电–气耦合系统(integrated electricity natural gas system,IEGS)的负荷重分配攻击可能会对系统的安全运行造成更严重的影响。因此本文对电–气耦合下的LR攻击展开深入研究。首先,在分析IEGS双侧协同LR攻击作用机理的基础上,研究LR攻击的实施策略。其次,计及连锁故障对电网的影响,以IEGS经济损失最大为目标函数,建立IEGS下LR攻击的损失评估模型,统一度量了不同能源子系统的损失,量化了不同场景下LR攻击对系统安全经济运行的风险,定义了新的节点综合脆弱性评价指标,全面深层次分析IEGS中的高脆弱性节点。再次,对天然气管道流量方程中的非线性项进行线性化处理,将IEGS调度模型转化并添加到攻击者模型中,作为Karush–Kuhn–Tucher(KKT)最优条件,从而将整个模型转换为混合整数线性规划问题。最后,在IEEE 39节点和改进比利时20节点算例系统上,进行了3种LR攻击场景的仿真,验证了3种攻击在不同攻击资源下的攻击效果,分析了系统高脆弱性节点的分布与变化,并给出了针对不同LR攻击形式的系统综合保护策略。实验结果表明,双侧协同LR攻击会对系统造成更严重的损失,但依据本文评估和分析方法采取综合保护策略后,系统损失显著降低。

考虑混氢天然气的综合能源系统低碳经济调度

提出考虑混氢天然气的电-气综合能源系统低碳经济调度策略,协同调度P2G设备中电制H2和电制CH4 2种电-气转换过程,以混氢天燃气(hydrogen enriched compressed natural gas,HCNG)的形式满足终端燃气需求,以改善系统的运行性能。经改进的IEEE 14节点电力网和比利时20节点天然气网耦合系统进行验证,结果表明,所提IEGS调度策略可在提高风电转换效率、实现碳减排的同时,保障用气需求,提升系统运行的经济性。

考虑压缩机不同运行状态的IES气网潮流分布式计算方法

压缩机运行状态的改变会造成气网工况变化,进而对电-气-热综合能源系统的稳态潮流产生影响。为求解压缩机不同运行状态下的综合能源系统气网潮流,文中分别对综合能源系统各子网络和能量耦合环节建模。考虑压缩机5种工作模式和2种驱动方式,针对含有多台不同运行状态压缩机的天然气网络,基于牛顿-拉夫逊法,提出保留压缩机管道整体求解的气网潮流计算方法,并拓展一种分离压缩机管道等效求解方法,以分布式计算方法顺序求解综合能源系统潮流。通过2个算例,验证了所提保留压缩机管道整体求解方法的精确性和有效性,弥补了现有气网潮流计算模型无法处理复杂气网工况且收敛性、通用性差的缺点,揭示了压缩机运行状态的改变对综合能源系统潮流的影响。